1. Field of the Invention
The present invention relates to an image blur prevention apparatus for preventing an image blur from occurring in cameras, optical equipment, and so on.
2. Related Background Art
Since recent cameras are automated as to all operations important for photography, including the determination of exposure, focusing, and the like, the possibility of causing faulty photography is very low even for people lacking in camera operational skills.
Systems for preventing hand vibration (fluctuation) from being transferred to the camera have been researched these years, and there now remains only a few factors which induce faulty photography.
In the following, a system for preventing hand vibration will be explained briefly.
The hand vibration experienced by a camera upon photography normally includes the fluctuation at frequencies of 1 Hz to 12 Hz, and the basic idea for enabling one to take a photograph without image blur even with such hand vibration occurring at a shutter release point is to detect the fluctuation of the camera due to the above hand vibration and to displace a correction lens in accordance with a value thus detected. In order to achieve the taking of a photograph without an image blur even where camera fluctuation occurs, it is thus necessary, first, to accurately detect the fluctuation of the camera and, second, to correct a change of the optical axis due to the hand vibration.
Fundamentally speaking, the detection of vibration (camera fluctuation) can be conducted by equipping the camera with a vibration detecting means for detecting an angular acceleration, an angular velocity, an angular displacement, or the like and a camera fluctuation detecting means for electrically or mechanically integrating an output signal from the foregoing sensor to output an angular displacement. Then the image blur can be suppressed by driving a correction optical mechanism for deviating the photographic optical axis, based on the detection information.
Now, an image blur prevention system using the vibration detecting means is schematically explained referring to FIG. 14.
The example of FIG. 14 is an illustration of a system for controlling the image blur originating from vertical fluctuation 81p and horizontal fluctuation 81y of a camera in the directions of arrows 81, as shown.
In the drawing, reference numeral 82 designates a lens barrel, and 83p, 83y donote vibration detecting means for detecting the camera vertical fluctuation and camera horizontal fluctuation, respectively, the directions of fluctuation detection of which are represented by 84p, 84y, respectively. Numeral 85 denotes a correction (optical) means (wherein 85p, 85y are coils for giving thrust to the correction means 85 and 86p, 86y are position detecting elements for detecting the position of the correction means 85), and the correction means 85 is provided with a position control loop described later to be driven using outputs from the vibration detecting means 83p, 83y as target values, thereby securing stability at the image plane 88.
FIG. 15 is an exploded perspective view to show the structure of the correction means suitably used for the above purpose, and this structure will be explained also referring to FIG. 16 to FIG. 23.
Back projection ears 71a [at three positions (one of which is on the blind side)] of a base plate 71 (an enlarged view of which is shown in FIG. 17) are brought into fit with the unrepresented barrel and conventional barrel rollers or the like are screwed to holes 71b, thereby fixing the base plate to the barrel.
A second yoke 72 being a magnetic member and covered with bright deposits is screwed to holes 71c of the base plate 71 by screws penetrating holes 72a. Further, permanent magnets (magnets for shift) 73 such as neodymium magnets magnetically adsorb to the second yoke 72. The directions of magnetization of the respective permanent magnets 73 are the directions of arrows 73a illustrated in FIG. 15.
Coils 76p, 76y (coils for shift) are in snap-fit adhesion (which means a state of adhesion after forcibly pushed into) to a support frame 75 (an enlarged view of which is shown in FIG. 18) to which a lens 74 is fixed through a C-ring or the like (though FIG. 18 shows a state before adhesion of the coils), and light projecting elements 77p, 77y, such as IREDs, are also bonded to the back face of the support frame 75. Light emitted from the light projecting element passes through a slit 75ap, 75ay to be incident on a position detecting element 78p, 78y, such as a PSD described hereinafter.
FIG. 16 is a lateral sectional view of the correction means after being assembled, and assembling of the correction means is next explained referring to the drawing.
Support balls 79b (at three positions) of a ball bearing or the like are temporarily set in holes 75b' of the support frame 75 by applying, for example, fluorine-based grease thereto. In this state, returning to FIG. 15, one end of an L-shaped shaft 711 (of a non-magnetic stainless steel material) is inserted, after coated with grease, into a bearing portion 75d of the support frame 75 and the other end is inserted into a bearing portion 71d (similarly coated with grease) formed in the base plate 71. Then, all support balls 79b at three positions are mounted on the second yoke 72 so as to set the support frame 75 in the base plate 71.
After that, charge springs 710, and support balls 79a of the ball bearing or the like are incorporated in order into the holes 75b of the support frame 75.
Next, for example, the fluorine-based grease is applied to the bearing portion 75d of the support frame 75, the L-shaped shaft 711 (of the non-magnetic stainless steel material) is inserted there (see FIG. 15), and the other end of the L-shaped shaft 711 is inserted into the bearing portion 71d (after similarly coated with the grease) formed in the base plate 71.
Then, positioning holes 712a (at three positions) of a first yoke 712 shown in FIG. 15 are brought into fit on pins 71f (at three positions) of the base plate 71 shown in FIG. 17, and receiving facets 71e (at five positions) also shown in FIG. 17 catch the first yoke 712 so as to magnetically couple it with the base plate 71 (by the magnetic force of the permanent magnets 73).
This makes the back face of the first yoke 712 go into contact with the support balls 79a and makes the support frame 75 sandwiched between the first yoke 712 and the second yoke 72, as shown in FIG. 16, to effect positioning in the direction of the optical axis.
The fluorine-based grease is also applied to the mutual contact faces between the support balls 79a, 79b and the first yoke 712 or the second yoke 72, and the support frame 75 is freely slidable within the plane perpendicular to the optical axis with respect to the base plate 71.
The charge springs 710 are charged against the first yoke 712, so that the lens 74 is biased toward the second yoke 72 to be stabilized in position.
The above L-shaped shaft 711 supports the support frame 75 so that it can slide only in the directions of arrows 713p, 713y with respect to the base plate 71, thereby regulating relative rotation (rolling) of the support frame 75 about the optical axis with respect to the base plate 71.
Fitting play between the above L-shaped shaft 711 and the bearing portions 71d, 75d is set rather great in the optical-axis direction, thereby preventing duplex fitting against the regulation in the optical-axis direction by pinching with the support balls 79a, 79b, the first yoke 712, and the second yoke 72.
The surface of the first yoke 712 is covered by an insulation-purpose sheet 714 and a hard board 715 having a plurality of ICs (the position detecting elements 78p, 78y, output amplifying ICs, ICs for driving the coils 76p, 76y, etc.) is set thereon so that positioning holes 715a (at two positions) are fit on pins 71h (at two positions) of the base plate 71 shown in FIG. 17. Then holes 715b are screwed together with the holes 712b of the first yoke 712 into the holes 71g of the base plate 71.
Here, the position detecting elements 78p, 78y are positioned with a tool and soldered on the hard board 715, and a flexible board 716 for transmission of signal is also fixed so that a surface 716a thereof is press-welded by heat to a range 715c (see FIG. 15) surrounded by the dashed line in the back face of the hard board 715.
A pair of arms 716bp, 716by project out in directions on the plane perpendicular to the optical axis from the flexible board 716 to be hooked on hook portions 75ep, 75ey (see FIG. 18), respectively, of the support frame 75, and the terminals of the light projecting elements 77p, 77y and the terminals of the coils 76p, 76y are soldered thereto.
By this arrangement, the driving of the light projecting elements 77p, 77y such as IREDs and the coils 76p, 76y is executed by the hard board 715 through the flexible board 716.
The arms 716bp, 716by (see FIG. 15) of the above flexible board 716 have respective bending portions 716cp, 716cy and the elasticity of the bending portions decreases loads of the arms 716bp, 716by on the motion of the support frame 75 in the plane perpendicular to the optical axis.
The first yoke 712 has projecting surfaces 712c formed by stamping, and the projecting surfaces 712c are in direct contact with the hard board 715 through holes 714a of the insulating sheet 714. A ground pattern is formed on the side of the hard board 715 in this contact surface, so that the first yoke 712 is a rounded by screwing the hard board 715 to the base plate, thereby preventing them from being an antenna and thus adding noise to the hard board 715.
A mask 717 shown in FIG. 15 is positioned by pins 71h of the base plate 71 and fixed on the hard board 715 by double-sided tape.
A through hole 71i a for permanent magnet (see FIG. 15 and FIG. 17) is formed through the base plate 71 and the back face of the second yoke 72 is exposed through the through hole. A permanent magnet 718 (magnet for lock) is incorporated in this through hole 71i to be magnetically coupled with the second yoke 72 (see FIG. 16).
A coil 720 (coil for lock) is bonded to a lock ring 719 (see FIG. 15, FIG. 16, and FIG. 19). Further, a bearing 719b (see FIG. 20) is located on the back face of an ear 719a of the lock ring 719, and an armature pin 721 (see FIG. 15) is put through an armature rubber 722 and then the armature pin 721 is set through the bearing 719b. After that, an armature spring 723 is put over the armature pin 721 and the pin is fit into an armature 724 to be fixed by calking.
Therefore, the armature 724 can slide in the directions of arrows 725 relative to the lock ring 719 against charge force of the armature spring 723.
FIG. 20 is a plan view of the correction means after completion of assembling, seen from the back side of FIG. 15. In this figure, the lock ring 719 is mounted to the base plate 71 by such conventional bayonet coupling that the lock ring 719 is pushed into the base plate 71 while keeping outer cut portions 719c (at three positions) of the lock ring 719 matched with inner projections 71j (at three positions) of the base plate 71 and thereafter the lock ring is rotated clockwise to effect locking.
Therefore, the lock ring 719 is rotatable about the optical axis with respect to the base plate 71. In order to prevent disengagement of the bayonet coupling with such rotation of the lock ring 719 as to make the cuts 719c again aligned in the same phase with the projections 71j, a lock rubber 726 (see FIG. 15 and FIG. 20) is pushed into the base plate 71, whereby rotation of the lock ring 719 is regulated so that the lock ring 719 can rotate only in the range of angle .theta. (see FIG. 20) of a cut portion 719d regulated by the lock rubber 726.
A permanent magnet 718 (magnet for lock) is attached also to a yoke 727 (see FIG. 15) of a magnetic member. Holes 727a (at two positions) of the yoke 727 are fit on pins 71k (see FIG. 20) of the base plate 71, and the yoke 727 and the base plate 71 are screwed through holes 727b (at two positions) and 71n (at two positions).
A well known closed magnetic circuit is formed by the permanent magnet 718 on the base plate 71 side, the permanent magnet 718 on the locking yoke 727 side, and the second yoke 72 and locking yoke 727.
Further, the above lock rubber 726 is prevented from slipping off by screwing of the locking yoke 727. The locking yoke 727 is not illustrated in FIG. 20, for the above explanation.
A lock spring 728 is hooked on between a hook 719e of the lock ring 719 and a hook 71m of the base plate 71 (see FIG. 20), thereby energizing the lock ring 719 clockwise. An adsorption coil 730 is put onto an adsorption yoke 729 (see FIG. 15 and FIG. 20) and is screwed through a hole 729a of the base plate 71.
The terminals of coil 720 and the terminals of adsorption coil 730 are arranged in a twisted pair structure of polyester-coated lines of four-wire strands to be soldered to a trunk 716d of the flexible board 716.
ICs 731p, 731y on the hard board 715 are ICs for amplifying outputs from the position detecting elements 78p, 78y, respectively, and the internal structure thereof is as shown in FIG. 21 (wherein only 731p is shown because the ICs 731p, 731y are constructed in the same structure).
In FIG. 21, current-voltage conversion amplifiers 731ap, 731bp convert photocurrents 78i.sub.1 p, 78i.sub.2 p, occurring in the position detecting element 78p (consisting of resistors R1, R2) because of the light projecting element 77p, into voltages and a differential amplifier 731cp obtains a difference output between the outputs from the current-voltage conversion amplifiers 731ap, 731bp to amplify it.
The light emitted from the light projecting element 77p, 77y is incident through the slit 75ap, 75ay onto the position detecting element 78p, 78y, as described previously, and the position of incidence onto the position detection element 78p, 78y changes when the support frame 75 moves in the plane perpendicular to the optical axis.
The position detecting element 78p has a sensitivity in the directions of arrows 78ap (see FIG. 15) and the slit 75ap is shaped so as to expand a beam in the directions (directions 78ay) perpendicular to the arrows 78ap and to converge the beam in the directions of arrows 78ap. Thus, a balance between the photocurrents 78i.sub.1 p, 78i.sub.2 p of the position detecting element 78p changes only when the support frame 75 moves in the directions of arrows 713p, and the differential amplifier 731cp gives an output depending upon movement of the support frame 75 in the directions of arrows 713p.
Further, the position detecting element 78y has its detection sensitivity in the directions of arrows 78ay (see FIG. 15), and the slit 75ay is shaped so as to extend in the directions (directions 78ap) perpendicular to the arrows 78ay. Thus, the position detecting element 78y changes its output only when the support frame 75 moves in the directions of arrows 713y.
A summing amplifier 731dp obtains the sum (the sum of quantities of received light by the position detecting element 78p) of the outputs from the current-voltage conversion amplifiers 731ap, 731bp, and a driving amplifier 731ep receiving this signal drives the light projecting element 77p according thereto.
The quantity of projected light from the light projecting element 77p changes on a very unstable basis depending upon the temperature or the like, and with the change an absolute quantity (78i.sub.1 p+78i.sub.2 p) of the photocurrents 78i.sub.1 p, 78i.sub.2 p of the position detecting element 78p changes. Because of this, the output from the differential amplifier 731cp, (78i.sub.1 p-78i.sub.2 p), indicating the position of the support frame 75, also changes.
However, the change of the output from the differential amplifier 731cp can be suppressed by controlling the light projecting element 77p by the aforementioned driving circuit so as to keep the sum of the quantities of received light constant as described above.
The coils 76p, 76y shown in FIG. 15 are located inside the closed magnetic circuit formed by the permanent magnets 73, first yoke 712, and second yoke 72. Thus, the support frame 75 is driven in the directions of arrows 713p (according to the Fleming's left-hand rule) with the flow of current through the coil 76p, and the support frame 75 is driven in the directions of arrows 713y with the flow of current through the coil 76y.
Generally, when the outputs from the position detecting elements 78p, 78y are amplified by the ICs 731p, 731y and the coils 76p, 76y are driven by outputs therefrom, the support frame 75 is driven to change the outputs from the position detecting elements 78p, 78y.
Here, when the driving directions (the polarities) of the coils 76p, 76y are set in such directions as to decrease the outputs from the position detecting elements 78p, 78y (in the negative feedback), the support frame 75 is stabilized at the position where the outputs from the position detecting elements 78p, 78y become nearly zero by the driving force of the coils 76p, 76y.
This driving technique, by negative feedback of position detection outputs, is called as a position control technique, and, for example, if target values (for example, hand-vibration angle signals) are mixed into the ICs 731p, 731y from the outside, the support frame 75 can be driven very loyally according to the target values.
In actual arrangement, the outputs from the differential amplifiers 731cp, 731cy are sent through the flexible board 716 to the main board not shown, in which analog-to-digital conversion (A/D conversion) is carried out. The results are taken into a microcomputer.
In the microcomputer the input signals are compared suitably with the target values (hand-vibration angle signals) to be amplified, phase lead compensation (for stabilizing the position control more) is effected by the conventional digital filter technique, and thereafter the signals are again input through the flexible board 716 to IC 732 (for driving the coils 76p, 76y). The IC 732 performs the well-known PWM (pulse-width modulation) drive of the coils 76p, 76y, based on the signals input thereto, thereby driving the support frame 75.
The support frame 75 can slide in the directions of arrows 713p, 713y as described previously, and is stabilized in position by the position control technique discussed above. However, for consumer-oriented optical devices including cameras, it is not allowed to always control the support frame 75 from the viewpoint of preventing waste consumption of power.
Since the support frame 75 becomes free to move in the plane perpendicular to the optical axis during a non-controlled state, it is necessary to provide a countermeasure against generation of colliding sound or damage at the stroke ends during that state.
As shown in FIG. 18 and FIG. 20, projections 75f radially projecting are provided at three positions on the back face of the support frame 75, and the tips of projections 75f are fit to the inner peripheral surface 719g of the lock ring 719 as shown in FIG. 20. Therefore, the support frame 75 is restrained in the all directions relative to the base plate 71.
FIGS. 22A and 22B are plan views to show the relation between the lock ring 719 and the operation of the support frame 75, which are drawings obtained by extracting only the major part from the plan view of FIG. 20. For making the explanation easier to understand, the layout is changed a bit from the actually assembled state. Further, cams 719f (at three positions) shown in FIG. 22A are not formed throughout the entire region in the direction of the generatrix of the cylinder of the lock ring 719, as shown in FIG. 16 and FIG. 19, and they are not seen actually along the viewing direction of FIGS. 22A, 22B. However, they are illustrated for explanation's sake.
As shown in FIG. 16, the coil 720 (where 720a denotes lead lines of four-wire strands guided around the outer periphery of the lock ring 719 by a flexible board or the not shown, and connected to the terminals 716e on the trunk 716d of the flexible board 716 from the terminals 719h) is set in the closed magnetic circuit between the permanent magnets 718, and generates torque for rotating the lock ring 719 about the optical axis when the current is supplied to the coil 720.
The drive of this coil 720 is also controlled by a command signal supplied from the unrepresented microcomputer through the flexible board 716 to the driving IC 733 on the hard board 715, and the IC 733 PWM-drives the coil 720.
In FIG. 22A the winding direction of the coil 720 is set so as to generate a counterclockwise torque in the lock ring 719 upon energization of coil 720, whereby the lock ring 719 rotates counterclockwise against the spring force of the lock spring 728.
Before energization of the coil 720, the lock ring 719 is stable in contact with the lock rubber 726 under the force of the lock spring 728.
With rotation of the lock ring 719, the armature 724 goes into contact with the adsorption yoke 729 as contracting the armature spring 723 so as to equalize the positional relation between the adsorption yoke 729 and the armature 724, whereby the lock ring 719 stops rotating as shown in FIG. 22B.
FIGS. 23A to 23C are timing charts of drive of the lock ring.
The coil 720 is energized (by the PWM drive indicated at 720b) at the arrow 719i of FIGS. 23A, and at the same time, the adsorption magnet 730 is also energized (at 730a). This causes the armature 724 to go into contact with the adsorption yoke 729 and to be equalized thereto and at that point the armature 724 is adsorbed to the adsorption yoke 729.
Next, when the energization of the coil 720 is stopped at the point indicated at 720c in FIGS. 23A to 23C, the lock ring 719 becomes about to rotate clockwise by the force of the lock spring 728. However, because the armature 724 is adsorbed to the adsorption yoke 729 as described above, the rotation is restrained. Since at this time the projections 75f of the support frame 75 are present at positions opposed to the associated cams 719f, the support frame 75 becomes capable of moving by a clearance between the projection 75f and the cam 719f.
This could cause the support frame 75 to drop in the direction of gravity G (see FIG. 22B), but the support frame 75 is also brought into the controlled state at the point of arrow 719i in FIGS. 23A to 23C, which prevents the support frame 75 from dropping.
In the non-controlled state the support frame 75 is restrained by the inner periphery of the lock ring 719, but it actually has play corresponding to the fitting play between the projections 75f and the inner peripheral wall 719g. Namely, the support frame 75 drops by this play in the direction of gravity G, so that there is an offset between the center of the support frame 75 and the center of the base plate 71.
Because of this control is carried out so as to move the support frame 75 to the center of the base plate 71 slowly, for example, during a period of one second from the point of the arrow 719i.
This is because if the support frame were moved quickly to the center, the photographer would sense fluctuation of image through the lens 74 which is discomforting and because even with exposure during this period there occurs no degradation of the image due to movement of the support frame 75. (For example, the support frame is moved 5 .mu.m per one eighth second.)
In more detail, the outputs from the position detecting elements 78p, 78y are stored at the point of arrow 719i in FIGS. 23A to 23C, control of the support frame 75 is started using the output values as target values, and for the period of one second thereafter the support frame 75 is moved for a target at the center of the optical system preliminarily set (see 75g in FIGS. 23A to 23C).
After the lock ring 719 is rotated (or unlocked), the support frame 75 is driven, based on the target values from the vibration detecting means (overlapping with the moving operation of the center position of the support frame 75 discussed above), thus starting the image blur prevention.
Here, when the image blur prevention is turned off at the point of arrow 719j in order to end the image blur prevention, the target values from the vibration detecting means are not input into the correction means, and the support frame 75 is stopped as controlled at the center position. Energization of the adsorption coil 730 is stopped at this point (730b). Then the adsorptive force of the armature 724 by the adsorption yoke 729 disappears so as to rotate the lock ring 719 clockwise by the lock spring 728 and to return it to the state of FIG. 22A. In this case, the lock ring 719 goes into contact with the lock rubber 726 to stop rotating, which controls the colliding sound of the lock ring 719 in the low level at the end of rotation.
After that, (for example, after 20 msec), the control on the correction means is interrupted so as to complete the timing chart of FIGS. 23A to 23C.
FIGS. 24A and 24B are block diagrams to show the scheme of the image blur prevention system.
In FIGS. 24A and 24B, reference numeral 91 designates the vibration detecting means 83p, 83y shown in FIG. 15, which is composed of a vibration detection sensor for detecting an angular velocity, such as a vibration gyro, and a sensor output arithmetic means for first cutting the DC component in the output from the vibration detecting sensor and thereafter integrating the output to obtain an angular displacement.
The angular displacement signal from this vibration detecting means 91 is input into a target value setting means 92. This target value setting means 92 consists of a variable differential amplifier 92a and a sample hold circuit 92b. Since the sample hold circuit 92b is always in a sampling state, two signals input into the variable differential amplifier 92a are always equal to each other and an output therefrom is zero. However, once the sample hold circuit 92b changes into a hold state by an output from a delay means 93 described hereinafter, the variable differential amplifier 92a starts continuously outputting as setting that point as zero.
An amplification factor of the variable differential amplifier 92a can be variably set by an output from an image blur prevention sensitivity setting means 94. The reason is as follows. The target value signal of the target value setting means 92 is a target value (command signal) which the correction means is allowed to follow, whereas a correction amount of the image plane against a drive amount of the correction means (image blur prevention sensitivity) changes depending upon optical characteristics based on a focus change of zooming, focusing, or the like. Therefore, the amplification factor is arranged as variable in order to compensate for the change of image blur prevention sensitivity.
Thus, the image blur prevention sensitivity setting means 94 takes in zoom focal-length information from a zoom information output means 95 and focus focal-length information based on distance measurement information from an exposure preparation means 96, calculates the image blur prevention sensitivity, based on the information, or extracts the information of image blur prevention sensitivity preliminarily set, based on the information, and changes the amplification factor of the variable differential amplifier 92a in the target value setting means 92.
The correction drive means 97 is the ICs 731p, 731y, 732 mounted on the hard board 715, and receives the target value from the target value setting means 92 as a command signal 730p, 730y.
A correction start means 98 is a switch for controlling the connection between the IC 732 on the hard board 715 and the coil 76p, 76y. In the normal condition, the switch 98a is connected to the terminal 98c to short both ends of each coil 76p, 76y. Receiving a signal from a logical product means 99, the switch 98a is connected to the terminal 98b to bring the correction means 910 into the control state (in which the fluctuation correction is not carried out yet but power is supplied to the coils 76p, 76y so as to stabilize the correction means 910 at the position where the signals of the position detecting elements 78p, 78y are almost zero). At the same time, the output signal from the logical product means 99 is input into an engagement means 914, whereby the engagement means releases engagement of the correction means 910.
The correction means 910 supplies the position signals of the position detecting elements 78p, 78y to the correction drive means 97 to effect the position control as described previously.
When the logical product means 99 receives both a release half press SW1 signal from a release means 911 and an output signal from an image blur prevention switching means 912, an AND gate 99a as a constituent component thereof outputs a signal. Namely, if the photographer manipulates the image blur prevention switch in the image blur prevention switching means 912 and if half press release is effected through the release means 911, the correction means 910 is released from engagement to turn into the control state.
The SW1 signal from the release means 911 is input into the exposure preparation means 96, whereby photometry, distance measurement, and lens focusing drive is carried out and whereby the focus focal-length information is input into the image blur prevention sensitivity setting means 94, as described previously.
The delay means 93 receives the output signal from the logical product means 99, and outputs it, for example, one second after to let the target value setting means 92 output the target value signals, as described above.
Although not shown, the vibration (fluctuation) detecting means 91 also starts in synchronization with the SW1 signal from the release means 911. As discussed previously, the sensor output arithmetic including a large time constant circuit, such as an integrator, requires some time from start before the output becomes stable.
The delay means 93 plays a role to wait before the output from the vibration detecting means 91 becomes stable and thereafter outputs the target value signals to the correction means 910 and is arranged to start the image blur prevention after the output from the vibration detecting means 91 is stabilized.
Receiving the release full press SW2 signal from the release means 911, an exposure means 913 moves the mirror up, effects exposure by opening and closing the shutter at a shutter speed obtained based on the photometry value of the exposure preparation means 96, and moves the mirror down, thereby completing photography.
After completion of photography, when the photographer moves the hand off the release means 911 to make the SW1 signal off, the logical product means 99 stops outputting to bring the sample hold circuit 92b in the target value setting means 92 into the sampling state and to make the output from the variable differential amplifier 92a zero. Thus, the correction means 910 returns into the control state with the correction drive being suspended.
Since the output of the logical product means 99 is turned off, the engagement means 914 effects engagement of the correction means 910 and thereafter the switch 98a of the correction start means 98 becomes connected to the terminal 98c, thus stopping the control of the correction means 910.
A timer, not shown, keeps the vibration detecting means 91 continuously operating for a certain period (for example, for five seconds) even after the stopping of manipulation of the release means 911, and then it is stopped. The reason of this is as follows. The photographer often again performs the release operation after the stopping of the release operation. In that case, the above arrangement can prevent the vibration detecting means 91 from being restarted every time the operation is preformed and can decrease the standby time before stabilization of the output therefrom. When the vibration detecting means 91 is already started, the vibration detecting means 91 sends an already-start signal to the delay means 93 to shorten the delay time.
The reason why the arrangement of the support balls 79a, 79b and the charge springs 710 as shown in FIG. 16 is adopted is that assembling is proceeded in such a state that the left side on the plane of FIG. 16 is set up, then the support balls 79b that can be temporarily fixed by grease are set down to keep the charge springs 710 and support balls 79a up upon assembling, thereby preventing these elements from dropping, and then the first yoke 712 is mounted thereon, whereby the support balls 79a, 79b and charge springs 710 can be prevented from dropping off from the support frame 75.
The charge force of the charge springs 710 is a resultant of forces at three positions as surpassing the force supporting the weights of the support frame 75 and lens 74, and thus urges the support frame 75 and lens 74 toward the second yoke 72 even though the correction means has any posture, thus stabilizing the optical system.
However, if the charge force of charge spring 710 were arranged to support the self-weight of the lens 74 at a position, slide friction would become greater against the first yoke 712 and the second yoke 72 in contact with the support balls 79a, 79b so as to obstruct smooth slide.
Therefore, it is desired to arrange the charge force of the charge springs 710 so as to stand for the self-weight of lens 74 by the resultant of forces at three positions and to such an extent that the charge spring at each position is just deflected by the self-weight of lens 74.
FIG. 16 shows a state in which the projections 75f of the support frame 75 are in a disengaged state from the internal peripheral wall 719g of the lock ring 719 and in which the support frame 75 is in an image-blur-prevention-controllable state and the support frame 75 is properly pinched with respect to the base plate 71.
FIG. 25 shows a lateral cross section where the support frame 75 is locked by the lock ring 719.
The center of gravity G of the total of the support frame 75 and lens 74 at this time is located as shown, and they are subject to the force due to gravity, directed from this position to the bottom of the plane of FIG. 25. Since the position where the lock ring 719 supports the support frame 75 (the engagement portion) is located on the right side in the plane of drawing with respect to the center of gravity, as shown by arrow 62, a couple of forces appear in the support frame 75 as directed in the direction of arrow 63 about the center at the sliding surface of support balls 79b indicated by arrow 61.
As long as the projections 75f of the support frame 75 firmly fit (or bite) the internal peripheral wall 719g of the lock ring 719 at the three positions, the above coupling appearingly gives no effect on the support frame 75 at all.
There is, however, some play provided between the projections 75f of the support frame 75 and the internal peripheral wall 719g of the lock ring 719 in the actual arrangement.
It is because if the support frame 75 should firmly fit the lock ring 719 the rotational load would be great on the lock ring 719 upon unlocking next.
Therefore, the projection 75f at the position of arrow 62 is in contact with the internal peripheral wall 719g in the state of FIG. 25 (because of gravity), while the projections 75f at the other two positions are not in contact with the internal peripheral wall 719g. If the coupling appears in the direction of arrow 63 shown in FIG. 25 in this state, nothing can stop the lens 74 from inclining because of the coupling. In other words, since the charge force per charge spring 710 is weak as discussed above, the couple deflects the spring, so that the support ball 79a goes down into the support frame.
Namely, there was the problem that the optical performance differed between in the controlled state where the correction means was disengaged with the image blur prevention being on and in the engaged state of the correction means with the image blur prevention being off.